Typical solenoid operated fuel injector design comprises an armature that impacts a stop when the electromagnetic coil of the solenoid is energized. A valve element attached to the armature is unseated from a valve seat to open the fuel injector when the coil is energized. When the coil ceases to be energized, a mechanical spring forces the armature away from the stop, causing the valve element to become reseated and thereby close the fuel injector. The impacting surface of the armature and the impacted surface of the stop are typically chrome plated both for impact resistance and for providing a non-magnetic interface between otherwise ferromagnetic parts. More precise flatness and parallelism of the impacting and impacted surfaces will discourage wear and as a consequence maintain original factory-set valve lift longer since the onset of impact-wear-induced increases in valve lift that begin to significantly alter the original factory-set flow characteristic will be postponed due to decreased impact wear.
Parallelism between the impacting and impacted surfaces is a function of tolerance stack-ups of various assembled parts and of tolerances in tooling used to assemble the parts. In a top-feed fuel injector where the lower end of the fuel inlet tube is the impacted stop surface, its parallelism to the impacting surface of the armature also relies on the rigidity of the valve housing.
Recent trends toward fuel injectors that are smaller in overall diameter have caused the valve housing to be considered as one of the parts whose diameter can be reduced. A thinner walled housing can make a significant contribution toward overall diameter reduction, but it will require more extensive, and hence more costly, machining to maintain parallelism between impacting and impacted surfaces of the armature and the fuel inlet tube respectively.
The present invention relates to a novel construction for a fuel injector that seeks to maintain a desired degree of parallelism between these impacting and impacted surfaces in conjunction with a reduction in the fuel injector's overall diameter. The invention reduces the significance of tolerances in their effect on the desired parallelism so that components do not have to be more extensively machined in order to achieve the desired degree of parallelism. In general the invention relates to a novel construction for joining the ferromagnetic valve body (which may be a single piece or an assembly of several pieces) with the ferromagnetic stator by means of a non-ferromagnetic member. The invention is herein disclosed by way of example in a top-feed fuel injector where the fuel inlet tube forms the ferromagnetic stator which has an annular end face that provides the stop face that is impacted by the armature.
From patents such as U.S. Pat. Nos. 4,915,350; 4,984,744; 5,165,656; 5,178,362; 5,217,204; 5,232,166; and 5,236,174, it is known to join a ferromagnetic valve body to a ferromagnetic fuel inlet tube by means of a tubular non-ferromagnetic member that is welded at one end to the inlet tube and at the other end to the valve body. However, in those constructions, the lower end of the non-ferromagnetic member is telescoped over the outside of the ferromagnetic valve body, and the telescopically engaged portions are united by welding in the radial direction at a location on the non-ferromagnetic member that is axially located at about the midpoint of the telescopically overlapping portion of the non-ferromagnetic member. In some of these patents such as U.S. Pat. No. 5,217,204, axial guidance of the armature is provided by an axial I.D. surface of the non-ferromagnetic member, and not the valve body, so that parallelism of the impacting end surface of the armature to the impacted end surface of the inlet tube appears to be determined by controlling the tolerances of only the fuel inlet tube and the non-ferromagnetic member where they telescope together. In other of these patents, such as U.S. Pat. No. 4,915,350, axial guidance of the armature is accomplished by a so-called "slide bore" that is a part of the valve body, but that has an axial length that is short in comparison to the axial length of the armature. This so-called slide bore is at the upper end of the I.D. of the valve body, and the remainder of the valve body bore, within which the lower end portion of the armature is disposed, intentionally has a larger I.D. so that it deliberately provides no guidance of the armature. The location of this so-called slide bore is axially even with or axially above the axial location where the non-ferromagnetic member and the valve body are telescopically engaged.
The present invention comprises a construction that is distinguished from those of the aforementioned patents in that the valve body is fitted to the non-ferromagnetic member by telescoping the upper axial end of the valve body over the O.D. of the lower end of the non-ferromagnetic member and by guiding the armature on the I.D. of a cylindrical guide surface in the valve body bore at a location that is axially below the axial location where the upper end of the valve body and the lower end of the non-ferromagnetic member telescopically engage. For given part tolerances and given tolerances in tooling that is used to assemble the parts, closer tolerance in parallelism of impacting to impacted surfaces is obtained with the invention.
The invention will be described in full detail in the ensuing description and claims which are accompanied by drawings that disclose an exemplary presently preferred embodiment of the invention according to the best mode contemplated at the present time for carrying out the invention. Various features and advantages of the invention will more fully appear as the disclosure proceeds.